1. Field of the Invention
The present invention is related to nuclear fuel elements and in particular to gas cooled nuclear fuel elements.
2. General Background
Gas-cooled particle bed reactors (PBR's) being considered for multi megawatt space power and propulsion applications in strategic defense initiative studies are cooled by a gas flowing radially inward through the annular particle bed. These reactors use fuel elements formed from particle fuel wherein the fuel particle bed is confined in the annular space between an outer porous cylinder and an inner porous cylinder. The coolant gas flows out of an axial channel defined by the inner porous cylinder. A variety of fuel elements and fuel particles are known in the art.
U.S. Pat. No. 3,992,258 entitled "Coated Nuclear Fuel Particles And Process For Making The Same" discloses coated nuclear fuel particles of low density to accommodate fission gases generated during the use of the fuel particles.
U.S. Pat. No. 3,928,132 entitled "Annular Fuel Element For High-Temperature Reactors" discloses a compacted fuel element of annular shape enclosed in a graphite casing constituted by an inner and outer tube. The outer tube is larger than the inner tube and also has a greater coefficient of shrinkage.
U.S. Pat. No. 3,361,638 entitled "Pyrolytic Graphite And Nuclear Fuel Particles Coated Therewith" disclosed a nuclear fuel particle having a central core of fissile or fertile material surrounded by a fission-product retentive layer of true pyrolytic graphite.
U.S. Pat. No. 3,311,540 entitled "Integral Boiling and Superheating Nuclear Reactor And Pressure Tube Assembly Therefor" discloses a direct cycle integral vapor generating and superheating reactor having, within each pressure tube, a plurality of concentric annular fuel elements clad in metal such as stainless steel. The coolant passes alternately downwardly and upwardly among the fuel elements from the outer flow passage to the inner flow passage.
U.S. Pat. No. 3,222,773 entitled "Process For Assembling Concentrically Spaced Nuclear Fuel Elements" discloses a process of assembly for arranging cladded tubular and cylindrical nuclear fuel members within each other.
U.S. Pat. No. 3,345,733 entitled "Nuclear Reactor Fuel Elements" discloses a method of constructing a nuclear fuel element of a plurality of part annular plates supported at their longitudinal edges by radial support members to define a series of spaced coaxial tubes.
U.S. Pat. No. 2,985,576 entitled "Fuel Element For Nuclear Reactor", U.S. Pat. No. 3,138,534 entitled "Fuel Arrangement For A Neutronic Test Reactor", U.S. Pat. No. 3,165,448 entitled "Nuclear Reactor Core And Fuel Assembly", U.S. Pat. No. 3,422,523 entitled "Process For Fabricating Nuclear Reactor Fuel Elements", and U.S. Pat. No. 3,753,854 entitled "Production Of A Fuel Carbide With A Jacket Of Fuel Nitride, Sulfide, or Phosphide" are representative of the art.
Calculations indicate that for uniformly loaded fuel elements the full potential power density of the peripheral fuel cannot be realized because of heat transfer and fuel temperature constraints in the hot region at the inner boundary of the fuel element.